One of the more common tasks in robotic assembly is the insertion of a peg or rod into a hole. Traditionally, this "peg-in-hole" type of assembly has been difficult to implement in the robotics realm. Although the assembly parts are usually beveled to facilitate the assembly process, misalignments can cause the peg to wedge or jam in the hole during insertion. In response to this problem, compliant devices have been designed which respond to the force generated at the point of contact between the misaligned parts. Generally, two types of compliance techniques are used, passive compliance and active compliance. A passively compliant device holding an assembly part is given a degree or several degrees of freedom such that the compliant device will deform in response to the contact force between the assembly parts, in such a way as to reduce the probability of jamming. An actively compliant device holding an assembly part is one which senses the contact force between the assembly parts and responds with active control to change the position of the part it is holding to reduce the contact force and ease the insertion process.
Perhaps the most widely used passively compliant technique is that of a Remote Center Compliance device (RCC). The RCC is constructed such that the transverse component of the assembly force, that is, the force component that is perpendicular to the peg/hole axis, does not cause the peg tip to rotate and therefore to misalign with the hole. In other words, the remote center compliance device being used in a peg-in-hole type assembly, resists the rotational effect of the force on the peg due to contact between the peg and the side of the hole, while allowing lateral movement of the peg relative to the hole. The practical realizations of the remote center compliance device have been based on the assumption that the compliance of the mating parts and/or the supporting jigs, fixtures, robots, grippers, etc. is small compared to that of the remote center compliance device. However, many assembly devices such as multi jointed robot arms have considerable rotational compliance. When this is the case, both the pin tip and the hole individually rotate by differing amounts under the action of the assembly force, thereby increasing angular misalignment and the probability of jamming.